1. The Field of the Invention
The present invention relates to a threaded fastener, such as a screw. More particularly, the present invention relates to a cannulated screw having a flattened tip to facilitate securement of bone, tissue, or other materials in a medical, industrial, or similar setting.
2. The Relevant Technology
Mechanical fasteners, such as screws, bolts, nails, and the like, have long been utilized in industrial, construction, medical, and other settings to facilitate the securement of one or more members in a desired placement or configuration. For example, screws can be utilized to secure lumber, metal braces, and other materials in a particular setting. Screws typically comprise a head, a threaded portion, and a tip. The head is typically configured to accommodate a rotational tool which provides the torque necessary to drive the screw into the material into which the screw is desired to be inserted. The tip and threads of the screw are designed to allow for self boring of the screw into the material into which it is to be inserted. The tip of the screw is configured to bore into the material in a manner that allows engagement of the threads within the material. The threads, once engaged by the material, provide a forward force to facilitate additional forward movement of the screw in a perpendicular vector relative to the front plane of the material.
One difficulty that is associated with existing screws, is that the tip of such screws typically have a fairly sharp point to allow for self tapping of the screw into the material. The pointed tip of the screw can have a variety of lengths and configurations based on the implementation for which the screw is designed. In many implementations, the length of such tips can be fairly long. For example, in some designs the length of the tip is approximately the equivalent of the distance between three threads along the shaft of the screw. The tip of the screw is typically sharpened such that as the user provides sufficient normal force, the sharpened tip will puncture sufficiently into the material to allow for the engagement of the threads in the material.
When a user is utilizing the screw to affix a member, board, or other material to a secondary member, once the screw has fully penetrated the material or member, the tip of the screw will then begin to enter the secondary member to which the primary member is being secured. As a result, the amount of normal force that is needed to begin self tapping of the tip of the screw into the secondary member will typically force the secondary member a certain amount of displacement away from the primary member resulting in a gap at the interface of the two members. Such gaps can be undesirable as the gaps can limit the strength and aesthetics of the bond between the two members. The gap resulting from the configuration and use of such screws can be problematic and frustrating to a user who is attempting to provide effective and close contact between the two members.
The configuration of the tip of such screws and the resulting gaps can be particularly problematic in a medical setting. One reason that such gaps can be undesirable is that, in a medical setting, screws are typically utilized to secure bone to bone or tissue or another material to bone. As a result, spacing or gaps between the bone securement interface can prevent secure bonding between the two pieces of bone. This can be particularly problematic where the two pieces of bone comprise fragments of a broken bone. Any space between the two bones can result in prolonged healing and complete ossification of the space between the bones which can result in changes to the shape of the bone. Such changes to the shape of the bone can alter the mechanics of the bone in a manner that could weaken or result in changes to the biomechanics of the user's body. Additionally, such spacing can result in abnormal growth in the bone that can create additional complications.
An additional complication that is created in the use of such screws in securing bone segments to one another relates to the nature of bones. Bone typically comprises an outer cortical portion and an inner cancellous bone layer. The cortical bone layer is substantially harder and stronger than the typically softer and more porous cancellous portion. As a result, the cortical bone provides the desired anchoring characteristics for embedding screws and other medical fasteners. While the cortical bone layer is stronger than the cancellous portion, the cortical portion is typically quite thin compared to the cancellous portion.
The cortical bone layer typically lies on the outer boundary of the bone. As a result, where a screw has been threaded through two different segments of bone, the tip of the screw will begin to exit from the outward cortical portion of the bone opposite the bone/bone interface before the threads of the screw have engaged the cortical layer. In other words, the threaded portion of the screw may not have entered the rearward cortical bone layer before advancement of the screw must be stopped. Protrusion of the tip of the screw past the outer boundary of the cortical bone layer can be quite problematic. For example, protrusion of the tip of the screw from the cortical bone layer may result in contact of the tip of the screw with connective tissue, muscle tissue, or other tissue adjacent the bone that may result in severe pain and/or complications in the patient as a result of placement of the screw. In other words, the configuration of many existing medical screw-type fasteners is ill-suited for the securement of bone to bone or other materials to bone within the body. Many industrial and construction type screw-type fasteners suffer from the same type of deficiencies in their desired use setting as that described with relation to screws utilized in medical settings.